@celliott147 - Thank you for your response, but it does not address the part of my question relating to non-DEP purchased devices devices that we now wish to add to our ABM.
We have acknowledged the new IOS 14 licence agreement issued on 16/09/20, albeit on 21/09/20. This delay appears to have removed the ability to assign devices manually to our ABM and MDM server. Even though the licence has been agreed to it has not reset out facility to add serial numbers to our ABM manually.
How do I get this reset by Apple? Who do I need to contact without going through the end user telephone queue?